PDCs and other ultra-hard compacts have been used for many years in drilling and machining. These compacts are a construction of two components: an ultra-hard “plate” and its attached substrate. In use the compact or the part to be machined is rotated at high speeds. The plate is hard and abrasive by nature, such that when it makes contact with a material while the compact or part to be machined is rotating, it grinds away that material. The substrate serves two major purposes: (i) it acts as a shock absorber, protecting the plate from impacts; and (ii) it acts as an interface between the plate and the rest of the tool by creating a physical connection.
Connecting the plate to the substrate is traditionally performed as a sintering operation. In this process, a compacted ultra-hard powder (e.g., diamond powder) is placed into a heat and pressure mold of the final compact. The substrate is placed into the mold on top of the powder. The mold is sealed. Large amounts of heat—enough to generate a temperature of about 1400° C. to 1500° C.—and large amount of pressure—roughly 500,000 psi to 1,000,000 psi—are applied, which causes the powder to compress and the binder in the substrate—which is generally metallic based, commonly using a tungsten carbide matrix and cobalt binder—to melt, allowing the substrate's materials to sweep (i.e., permeate and fill the interstitial spaces) through the diamond powder. Cobalt metal is often used as a catalyst additive in the substrate because it catalytically promotes surface-to-surface bonds between diamond grains. The bonds formed are generally traditional sp3-hybridized, tetrahedral carbon-to-carbon bonds found in diamond creating a diamond-skeleton plate. This locks the shape of the plate, creating particles having bonds to adjacent particles. Localized pockets (due to filled interstitial spaces from the powder) are filled with binder or a carbide of the binder due to reaction with graphite formed from the diamond as a byproduct of this process. The net result is a dramatic increase in abrasion resistance under atmospheric conditions because of this catalyst.
A conventional end product is shown in FIGS. 1 and 2. PDC 100 comprises a diamond plate 110 and a substrate 120. The diamond plate has a rake 114—that is not responsible for cutting but instead helps remove cut material—and flank 112, which performs abrasion. The diamond plate 110 and the substrate have an interface 130.
Compacts made by this method demonstrate excessive wear. In use, these compacts are exposed to friction-inducted and environment-induced high temperatures, such as 700° C. or even higher. Such high temperatures will cause thermal expansion of compact. The binder's catalyst—such as cobalt, which as noted above is important for manufacture—generally has a significantly higher coefficient of thermal expansion (“CTE”) than diamond. Therefore, during use at high temperatures, large amounts of internal stress are put into the compact. This causes micro-cracks in the plate and results in significantly higher deterioration in abrasion resistance than would otherwise be demonstrated, increasing the probability of failure.
In order to overcome this deficiency, using a catalyst that has a similar CTE as diamond would obviate this concern. Silicon, for example, reacts with the diamond during the high temperature and high pressure step of compact sintering to form silicon carbide. Both silicon and silicon carbide exhibit a CTE relatively similar to diamond. Therefore, the resultant compact is considered thermally stable because it can withstand temperatures as high as 1100° C. without significant deterioration of abrasion resistance. (See U.S. Pat. No. 8,020,644, which is incorporated herein by reference.) However, PCD made utilizing silicon as a binder does not have similar properties to PCD made utilizing catalytic cobalt. Instead of forming diamond-to-diamond sp3 bonds between adjacent diamond grains (through bridges based on carbon-carbon bonds), the large majority of diamond grains are attached to each other through silicon bridges based off of silicon-carbon bonds. While carbon atoms at the surface of adjacent diamond grains may still form carbon-carbon bonds due to limited graphitization, silicon acts as the major bridge linking the diamond grains together. Silicon-carbon bonds have significantly less strength than the carbon-carbon sp3 bonds, and therefore the overall structure of the TSP formed with silicon binder is weaker than that formed utilizing catalytic cobalt.
Another method of overcoming the different CTE of the binder's catalyst and the diamond in the face is catalyst-leaching (e.g., an acid treatment to leach cobalt). This method has been performed such that little-to-no cobalt remains in the plate. This technique has been shown to significantly improve plate thermal effects on abrasion resistance of the plate, at the cost of increasing the brittleness of the plate. (See U.S. Pat. Nos. 4,104,344, 4,288,248, and 8,020,644, all of which are incorporated by reference.) This is one method to achieve a thermally stable polycrystalline (“TSP”). However, this method also deteriorates the usually-metallic substrate due to acid corrosion. Therefore, care should be taken to protect the substrate from acid corrosion while leaching the PDC, or other manufacturing steps are necessary in order to prepare the leached compact for use.
Using a high temperature, high pressure process (“HTHP”) again to add a new substrate would reintroduce cobalt back into the plate. This would render the leaching step insignificant. Therefore, this is not a reasonable method.
Attachment of the two components can be done using a braze joint (FIG. 3). PDC 300 comprises diamond plate 310 and substrate 320. The diamond plate 310 has rake 314 and flank 112. Importantly braze 332 connects substrate 320 and diamond plate 310, acting as an interface and mechanical attachment mechanism. However, conventional braze joints like braze 332 do not provide adequate bond strength between the plate and the substrate. In particular, the shear strength for a commercially available braze is between 20,000 and 35,000 psi. Such bond strength is insufficient for demanding applications, such as subterranean drilling.
Therefore relying solely on the conventional braze joint to provide adequate bond strength to hold both components together is insufficient and not desirable. It is also desirable to improve the attachment strength between a TSP plate and the substrate to allow the compact to handle demanding applications.